Deformed dose restoration to account for tumor deformation and position changes for adaptive proton therapy

Abstract

Background Online adaptation during intensity‐modulated proton therapy (IMPT) can minimize the effect of inter‐fractional anatomical changes, but remains challenging because of the complex workflow. One approach for fast and automated online IMPT adaptation is dose restoration, which restores the initial dose distribution on the updated anatomy. However, this method may fail in cases where tumor deformation or position changes occur. Purpose To develop a fast and robust IMPT online adaptation method named “deformed dose restoration (DDR)” that can adjust for inter‐fractional tumor deformation and position changes. Methods The DDR method comprises two steps: (1) calculation of the deformed dose distribution, and (2) restoration of the deformed dose distribution. First, the deformable image registration (DIR) between the initial clinical target volume (CTV) and the new CTV were performed to calculate the vector field. To ensure robustness for setup and range uncertainty and the ability to restore the deformed dose distribution, an expanded CTV‐based registration to maintain the dose gradient outside the CTV was developed. The deformed dose distribution was obtained by applying the vector field to the initial dose distribution. Then, the voxel‐by‐voxel dose difference optimization was performed to calculate beam parameters that restore the deformed dose distribution on the updated anatomy. The optimization function was the sum of total dose differences and dose differences of each field to restore the initial dose overlap of each field. This method only requires target contouring, which eliminates the need for organs at risk (OARs) contouring. Six clinical cases wherein the tumor deformation and/or position changed on repeated CTs were selected. DDR feasibility was evaluated by comparing the results with those from three other strategies, namely, not adapted (continuing the initial plan), adapted by previous dose restoration, and fully optimized. Results In all cases, continuing the initial plan was largely distorted on the repeated CTs and the dose‐volume histogram (DVH) metrics for the target were reduced due to the tumor deformation or position changes. On the other hand, DDR improved DVH metrics for the target to the same level as the initial dose distribution. Dose increase was seen for some OARs because tumor growth had reduced the relative distance between CTVs and OARs. Robustness evaluation for setup and range uncertainty (3 mm/3.5%) showed that deviation in DVH‐bandwidth for CTV D95% from the initial plan was 0.4% ± 0.5% (Mean ± S.D.) for DDR. The calculation time was 8.1 ± 6.4 min. Conclusions An online adaptation algorithm was developed that improved the treatment quality for inter‐fractional anatomical changes and retained robustness for intra‐fractional setup and range uncertainty. The main advantage of this method is that it only requires target contouring alone and saves the time for OARs contouring. The fast and robust adaptation method for tumor deformation and position changes described h...

A fast and robust constraint-based online re-optimization approach for automated online adaptive intensity modulated proton therapy in head and neck cancer

“…( 2) Online re-optimization strategies adapt the original plan to obtain similar or improved plan quality, without aiming at reproducing the original dose distribution (Botas et al 2018, Bobić et al 2021, Lalonde et al 2021. (3) Online dose restoration strategies adapt the original plan to obtain a similar dose distribution for the daily anatomy (Bernatowicz et al 2018, Borderías-Villarroel et al 2022, Miyazaki et al 2022. (4) Plan library strategies do not adapt the original plans.…”